The present invention is related to a method for the active damping of vibrations on and/or in a drive train of a wind energy plant.
With drive train is usually meant the assembly of rotor, rotor shaft (slow shaft), gearbox, generator shaft (fast shaft), coupling and generator. For wind energy plants, it is commonly known that the vibration excitations of the drive train may have different causes. First of all, circulation periodic disturbances are a possibility, like tower wind shelter or tower dam, height profile of the wind speed, skew upwind of the rotor through yaw angles or skew axis inclinations and/or unbalanced masses of the rotor blades. Besides to the outer excitations, which occur as multiples of the rotor's rotational speed, disturbances at the generator side also occur, like grid errors, electric grid oscillations at very long grid feed lines, oscillations of converters and DC intermediate circuits, control influences and consumer retroaction in the isolated operation. An overview about the vibration excitation and the resonances occurring with it is found in the textbook of Erich Hau, Windkraftanlagen, 3th edition, Springer-Veilag Berlin, chapter 11.2.4, the entire contents of which is incorporated herein by reference.
From WO 2004/112234 A1, the entire contents of which is incorporated herein by reference, a method for damping a torsional vibration on a rotating drive train is known. A damping device is provided for damping in this, which is tuned to a resonance frequency of the torsional vibration. The tuning must not deviate more than 3% from the resonance frequency of the drive train.
From EP 1 643 122 A2, the entire contents of which is incorporated herein by reference, a damping system for wind energy plants with variable speed is known. The damping system acquires the actual value of the rotational speed at the generator shaft. The actual value is forwarded to a control unit, which depending from the rotational speed determines a desired value for the torque on the generator. In order to avoid vibrations, a vibration damper is provided, the parameters of which are adapted depending from the resonance frequency of the drive train, a resonance for tower vibrations and from the movement of the rotor blade past the tower. A signal is connected to the vibration damper as an input, which is a measure for the generator rotational speed and which is amplified in order to generate a response signal. In order to adapt the vibration damper, a detection device is provided, which continuously calculates the resonance frequency of the tower and of the drive train and forwards the calculated values to the damper. In doing so, the detection device periodically scans the generator rotational speed. Vibrations cause changes of the generator rotational speed, which are transformed from the time region into the frequency region by the detection device. The frequency signals are forwarded to the vibration damper.
The present invention is based on the objective to provide a method for the active drive train damping, which reliably permits a damping with simple means.